Browsing by Author "Leiva Yamaguchi, Valeria"

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    A semiparametric Bayesian model for multiple monotonically increasing count sequences
    (2016) Leiva Yamaguchi, Valeria; Quintana Quintana, Fernando
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    New contributions to joint models of longitudinal and survival outcomes : two-stage approaches
    (2021) Leiva Yamaguchi, Valeria; Silva, Danilo Alvares da; Pontificia Universidad Católica de Chile. Facultad de Matemáticas
    Joint models of longitudinal and survival outcomes have gained much popularity over the last three decades. This type of modeling consists of two submodels, one longitudinal and one survival, which are connected by some common term. Unsurprisingly, sharing information makes the inferential process highly time-consuming. This problem can be overcome by estimating the parameters of each submodel separately, leading to a natural reduction in the complexity of joint models, but often producing biased estimates. Hence, we propose different two-stage strategies that first fits the longitudinal submodel and then plug the shared information into the survival submodel. Our proposals are developed for both the frequentist and Bayesian paradigms. Specifically, our frequentist two-stage approach is based on the simulation-extrapolation algorithm. On the other hand, we propose two Bayesian approaches, one inspired by frailty models and another that uses maximum a posteriori estimations and longitudinal likelihood to calculate posterior distributions of random effects and survival parameters. Based on simulation studies and real applications, we empirically compare our two-stage approaches with their main competitors. The results show that our methodologies are very promising, since they reduce the estimation bias compared to other two-stage methods and require less processing time than joint specification approaches.
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    New insights from GWAS on BMI-related growth traits in a longitudinal cohort of admixed children with Native American and European ancestry
    (CELL PRESS, 2023) Vicuña, Lucas; Barrientos, Esteban; Norambuena, Tomás; Alvares, Danilo; Gana Ansaldo, Juan Cristóbal; Leiva Yamaguchi, Valeria; Meza, Cristian; Lorenzoni Santos, José Guillermo; Mericq, Verónica; Pereira, Ana; Eyheramendy, Susana
    Body-mass index (BMI) is a hallmark of adiposity. In contrast with adulthood, the genetic architecture of BMI during childhood is poorly understood. The few genome-wide association studies (GWAS) on children have been performed almost exclusively in Europeans and at single ages. We performed cross-sectional and longitudinal GWAS for BMI-related traits on 904 admixed children with mostly Mapuche Native American and European ancestries. We found regulatory variants of the immune gene HLA-DQB3 strongly associated with BMI at 1.5 - 2.5 years old. A variant in the sex-determining gene DMRT1 was associated with the age at adiposity rebound (Age-AR) in girls (P = 9.8 x 10(-9)). BMI was significantly higher in Mapuche than in Europeans between 5.5 and 16.5 years old. Finally, Age-AR was significantly lower (P = 0.004) by 1.94 years and BMI at AR was significantly higher (P = 0.04) by 1.2 kg/m(2), in Mapuche children compared with Europeans.